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Clinical Investigation and Outcomes Research

Research Using Existing Databases

Marcia A. Testa, MPH, PhD

Department of Biostatistics

Harvard School of Public Health

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Accessing and Using Existing Clinical Research and Health

Outcomes Databases• A large number of existing databases are available

to clinical and health outcomes researchers– public access – limited or restricted-use data

• Public access data bases require no prior approval or fee and most often can be downloaded from the internet

• Limited and/or restricted use databases require approval application, fee or both

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Sources of Public Access Research Databases

• Common sponsors of public access databases are in the United States– Center for Disease Control and Prevention (CDC)– National Institutes of Health– Bureau of the Census– Agency for Health Care Research and Quality– Health and Human Services Agencies

• World Health Organization• General Practice Research Database of the UK

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How Do I Get the Data?

• Before downloading and analyzing data you must spend considerable time learning about the data and formulating your research hypothesis

• Sampling schemes, data collection methods, sampling weights and appropriate statistical routines should all be considered

• Most databases and documentation can be ordered on tapes (older data), CD’s or by downloading the data from the internet

• However, the data is not “READY” straight off the shelf

5Click here

Medicare Health Outcomes Survey

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Click Here

http://www.hosonline.org/surveys/hos/download/HOS_2006_Survey.pdf

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Medicare HOShttp://www.hosonline.org/surveys/hos/hosdata.aspx

8http://www.gprd.com/home/default.asp

General Practice Research Database United Kingdom

9http://www.cdc.gov/nchs/

CDC National Center for

Health Statistics

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CDC National Center for

Health Statistics

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CDC National Center for

Health Statistics

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NCHS Research Data Center

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NHANES

• The National Health and Nutrition Examination Survey (NHANES) is a program of studies designed to assess the health and nutritional status of adults and children in the United States.

• The survey is unique in that it combines interviews and physical examinations.

• Began in 1960’s and the diseases studied include:• Anemia , Cardiovascular disease, Diabetes, Environmental exposures,

Eye diseases, Hearing loss, Infectious diseases, Kidney disease, Nutrition, Obesity, Oral health, Osteoporosis, Physical fitness and physical functioning, Reproductive history and sexual behavior, Respiratory disease (asthma, chronic bronchitis, emphysema), Sexually transmitted diseases, Vision

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As Example of Research using the NHANES Database

Original Research Problem

April, 2010

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•http://www.cdc.gov/nchs/tutorials/NHANES/index_current.htm

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By clicking on each on of the links you will be instructed how to navigate and prepare your dataset.

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In the “Data Structure and Contents Module” you will be shown the general layout of the data files.

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Data and Documentation – NHANES 2007 - 2008

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Laboratory Files

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Questionnaire Files

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Demography File

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CRP, HbA1c, Cardiac Symptoms

• Investigate the relationships between– C Reactive Protein (CRP)– HbA1c– Symptoms of Heart Disease (Pain in

Chest) – Demographic Characteristics of age and

gender

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CRP, HbA1c, Cardiac Symptoms

• Is higher HbA1c associated with higher CRP levels?– in males– In females

• Are cardiac self-reported symptoms (e.g., chest pain) associated with higher CRP levels?

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Download Files

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Merge Files into Statistical Package (e.g. SPSS)

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Descriptive Statistics

• Merge four files– Demography– CRP– HbA1c– Cardiac Symptoms Questionnaire

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Positively Skewed

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Glycohemoglobin %

More Normally Distributed

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Are CRP and HbA1c Correlated?

• The higher CRP, the higher HbA1c

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CRP Quartiles

Divide sample into quartiles based upon CRP levels

CRP Quartiles

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HbA1c by CRP Quartiles

CRP Quartiles

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Is there a difference between Males and Females?

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Is there a difference between Males and Females?

• Females have a higher CRP (p < 0.0001) • HbA1c levels are slightly lower (p = 0.061)

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Is there a difference between Males and Females after controlling for age?

• Age is slightly higher in females – so control for age in analysis

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Is there a difference in CRP between Males and Females after controlling for age?

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Is there a difference between Males and Females after controlling for age?

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Cardiac Symptoms Questionnaire and CRP

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Cardiac Symptoms Questionnaire and CRP

Significant symptom and (gender X symptom) interaction

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Cardiac Symptoms Questionnaire and CRP

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Cardiac Symptoms Questionnaire and CRP

Interaction

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Investigate Further

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Cardiac Symptoms Questionnaire and CRP

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Cardiac Symptoms Questionnaire and CRP

Compare 1st and 4th Quartiles with respect to Chest Pain

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Cardiac Symptoms Questionnaire and CRP

Compare 1st and 4th Quartiles with respect to Chest Pain

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Cardiac Symptoms Questionnaire and CRP

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Cardiac Symptoms Questionnaire and CRP

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Summary

• Clinical research using existing databases is an excellent way to practice your research skills, while at the same time testing original hypotheses – potentially to be published

• Data quality is excellent, data is either at no cost or low cost and is immediately available